I tried looking up what Mengzi might mean in Brazil (or alternatively, in Portuguese) and couldn't find anything. Would you mind elaborating?

Possibly from https://www.dicionarioinformal.com.br/mengar/ ?

Just an aside, it's really bizarre that it's transliterated as Mengzi in the article. IMO, it would be much better to use the translation (Master Meng) or the far more common and more recognizable Mencius (which is at least mentioned).

> Just an aside, it's really bizarre that it's transliterated as Mengzi in the article.

Scholars over at least the last 15 years have been trending towards preferring Mengzi and Kongzi over Mencius and Confucius. 孟子 is "Mèngzǐ" not "Mencius"